Frequency dividers generally are circuits which receive an input signal having a first frequency and in response thereto output an output signal having a second frequency, the second frequency corresponding to the first frequency divided by a divider factor. The divider factor may be an integer value (like 2, 3, 4 etc.), in which case the frequency divider is also referred to as integer divider. In other cases, the divider factor may be a non-integer value (for example 2.5), in which case the frequency divider is also referred to as fractional divider.
Such frequency dividers are used in a variety of circuits for example to generate clock signals having a predefined frequency (frequency synthesis) based on some reference clock source like a crystal oscillator. For example, for such frequency synthesis a phase-locked loop (PLL) may be used. In such PLLs, a reference signal, for example generated by a crystal oscillator or other stable oscillation source, is compared with a feedback signal. A result of the comparison is filtered and used to control an oscillator like a voltage-controlled oscillator (VCO) or a digitally controlled oscillator (DCO). An output signal of the oscillator is fed to a frequency divider to form the feedback signal. This for example may lead to an output frequency of the oscillator being regulated to a frequency value corresponding to the frequency of the reference signal times the divider factor. Also in other applications where frequencies need to be converted, frequency dividers may be used.
In such applications, for example frequency synthesis, reliable and precise operation of the frequency divider is required. In particular, for some applications it may be required that the frequency divider operates reliably over varying operating conditions like temperature or supply voltage. With some frequency divider designs, an accuracy or reliability of the frequency divider may depend on a current supplied to the frequency divider. On the other hand, for example in battery-powered mobile applications or other low power applications it is desirable to reduce the current consumed by a frequency divider.